Sequential Nucleophilic Acyl Substitution/Alkenyl Transfer Reactions Mediated by Samarium(II) Iodide
Samarium(II) iodide (SmI2) has been employed in a one-pot, three-step, nucleophilic acyl substitution/ketyl−olefin coupling/β-elimination reaction sequence. This novel protocol combines two recently developed SmI2-mediated processes to permit the net delivery of an alkenyl moiety to a ketone carbonyl generated as an intermediate along the sequential reaction pathway. A remarkable measure of stereocontrol over three to five contiguous stereocenters is established in the process as a result of the excellent facial selectivity conveyed in the ketyl−olefin coupling reaction. Unique to the SmI2-mediated process, the relative asymmetric induction engendered in these addition reactions is complementary to more traditional nucleophilic addition reactions in that the alkenyl group is delivered to the carbonyl center by an attached tether. Moreover, the protocol avoids the basic reaction conditions characteristic of alkenylmagnesium halides and alkenyllithium reagents.